The document discusses concurrency and parallelism in Scala. It notes that manually handling threads and locks is difficult and error-prone. Actors provide a safer model for concurrency by encapsulating state and message-passing. Parallelism can be achieved in Scala through parallel collections that split work over multiple processors. The author advocates building asynchronous systems using actors for concurrency and parallel collections for parallelism to fully utilize hardware resources.

1. Concurrency and
Parallelism with Scala
Timothy Perrett
BrisFunctional, June 2011
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2. About Me
 Big Scala Geek
 Author of Lift in Action
 Coding Scala since 2007
 Background in both dynamic
and statically typed languages
 Manufacturing and marketing
automation is my day job
h"p://manning.com/perre"/
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3. Concurrency
vs
Parallelism
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4. Concurrency
Mutable state is
Plain Evil
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5. Concurrency
Threads and Locks
are EOL
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6. Concurrency
Actors to
the Rescue
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7. Concurrency
msg msg
msg msg msg
Mailbox
msg
Actor
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8. Concurrency
 Simpler mental model
 Much easier to avoid common issues:
 Deadlocks
 Race Conditions
 Starvation
 etc
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9. Concurrency
case class Increment(amount: Int)
class Counter extends Actor {
private var count = 0
def receive = {
case Increment(by) =>
count += by
println(count)
}
}
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10. Concurrency
val counter = actorOf[Counter]
counter.start
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11. Concurrency
counter ! Increment(10)
Fire
and
forget
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12. Concurrency
counter !!! Increment(10)
Fire
yielding
a
Future
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13. Concurrency
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14. Concurrency
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15. Concurrency
Don’t Block.
Ever.
(it’s
a
zen
thing)
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16. Parallelism
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17. Parallelism
Collections
on crack i-core
____________
Mult
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18. list.filter(predicate)
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19. list.filter(predicate).par
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20. Parallelism
Create
small
units
of
work
to
split
over
available
processor
capacity
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21. Parallelism
Stolen!
Processor A Processor B
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22. Plain
Lazy
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23. Not 100%
Toll Free
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24. Summary
 Manually handling threads and locks sucks
 Actors provide a sane model for concurrency
 Build completely asynchronous systems
 Get the most out of your hardware investment
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25. Further Reading
 Scala Language
http://scala-lang.org
 Akka Actor Toolkit
http://akka.io/
 State: You’re Doing It Wrong
http://www.slideshare.net/jboner/state-youre-doing-it-wrong-javaone-2009
 A Generic Parallel Collection Framework
http://infoscience.epfl.ch/record/150220/files/pc.pdf
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26. Questions?
twitter.com/timperrett Lift in Action
github.com/timperrett manning.com/perrett/
blog.getintheloop.eu
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